1. Field of the Invention
The present invention relates to a program for optometry, a recording medium and a subjective optometric apparatus having the optometric program, and an optometric method.
2. Description of the Related Art
In general, a subjective optometric apparatus which has a main body provided with a pair of right and left optometric units which are disposed so as to be capable of adjusting an interval therebetween, and a target displaying device which is visibly recognized by an examinee via optometric windows of the optometric units is known (for example, see Japanese Patent Application Publication No. 2002-143092).
In the subjective optometric apparatus of this type, a plurality of test lenses, polarizing plates, and other optical devices to be selectively disposed on each of the optometric windows are provided in the optometric units. As one of such optical devices, for example, a rotary prism used to carry out a prism correction for heterophoria or heterotropia is known.
In performing the above-mentioned prism correction for heterophoria or heterotropia, generally an amount of heterophoria of the examinee is first determined. Next, a fusional force of the examinee is determined and the prism correction is performed if it is found out that the determined fusional force cannot adequately compensate the heterophoria amount of the examinee.
In this case, as criterion for identifying whether the fusional force can adequately compensate the heterophoria amount of the examinee, Sheard criterion and Percival criterion are widely known.
In the case of the Percival criterion, it is required that both of a convergence force and a divergence force of the examinee be measured regardless of whether an ocular deviation of the examinee has an inward or an outward direction. The examinee is burdened with these examinations since they take such a long time.
On the other hand, in the case of the Sheard criterion, it is required that the fusional divergence reserve of the examinee be measured if the ocular deviation of the examinee is in the inward direction, and the fusional convergence reserve of the examinee be measured if the ocular deviation is in the outward direction. Therefore, the examinations based on the Sheard criterion reduce the burden imposed on the examinee and allow a greater reduction in time in comparison with that of the Percival criterion.
However, a relationship among the heterophoria amount, an amount of the convergence or the divergence of the examinee, and values of the Sheard criterion are not always known by an examiner. In practice, these examinations are sometimes not performed and unsuitable values are prescribed.
Furthermore, although conventional system optometric devices allow a convergence or divergence test for identifying the criterion of Sheard or Percival to be performed, they have no function for calculating an amount of a prism suitable for a prescription based on the criterion values.